Explanation:
In first case, the forces on LHS and on RHS is the same i.e. 3 N. The force acting on the car is balanced force. As a result, the car will not move at all.
In second case,
Force on RHS = 2000 N
Force on LHS = -6000 N
Net force acting on it is given by :
F = 2000+(-6000)
= -4000 N
Hence, this is the required solution.